JPS58147445A - Polyethylene composition for rotation formation - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] The present invention is a crosslinkable polyethylene composition.

In particular, it relates to such compositions which can be used in rotational molding processes. In particular, the present invention relates to rotomolded, crosslinkable polyethylene compositions that are substantially free of air bubbles and have good low temperature impact resistance.

The rotational molding process involves feeding a powdered polyethylene composition into a mold, then rotating the mold uniaxially, or usually biaxially, while simultaneously heating the mold from the outside to melt the layer of powdered polyethylene composition. The mold is cooled to solidify the fused material, and the product obtained by single rotation molding is removed from the mold.

Rotational molding is known and widely used for manufacturing hollow products, especially large hollow products with complex shapes and sizes, such as gasoline φ tanks, barrels, containers, storage tanks, etc. In order to make a commercially acceptable product using zero revolution molding, which can produce large products with uniform wall thickness, the polyethylene composition used in the process must, when melted, It is important to have melt flow characteristics that produce a uniform layer inside the melt. At the same time, however, the melt flow properties of the composition must be such that the resulting product has acceptable end use properties, particularly acceptable low temperature impact properties and environmental stress cracking resistance.

One method of improving the end-use properties of rotomolded products from polyethylene is to incorporate cross-linking agents, such as peroxides, into the polyethylene composition. In the rotational molding process of such compositions, the polyethylene flows to evenly coat the inside of the mold, and then the crosslinking agent crosslinks the polyethylene to increase the molecular weight of the resulting polymer. The end-use properties of the product are improved.

The use of polyethylene compositions containing cross-linking agents in the rotary molding process is known, for example in R.L., June 14, 1977.

U.S. Pat. No. 4,029,729 to Ree et al. discloses a method for rotomolding polyethylene comprising homopolymers or copolymers of ethylene having a melting coefficient of at least about 10 d g/min and containing an acetylene dioxy compound as a cross-linking agent. is listed. The molded articles obtained have a high degree of impact strength and are resistant to stress cracking. acetylene·
Although rotomolding resins containing dioxy compounds are commercially available, at least some such dioxy compounds are irritating to the skin and eyes, and as such are potentially hazardous to rotomolders. Known to be a health hazard.

D.G. Needham, April 8, 1975
US Pat. No. 3,876,613 to G., Needham et al. describes ethylene polymers that can be rotomolded to produce products with high impact strength. The composition contains both an acetylene dioxy compound and an ester of thiodipropionic acid.

It is also known to use cross-linkable polyethylene compositions containing both polyethylene and rubber or elastomeric products in rotational molding processes.
U.S. Patent No. 426 to Yokoyama et al., dated May 12, 1981.
No. 7080 contains 5-
50 parts by weight of goto and/or gills, stomers, sauer peroxide as a cross-linking agent, and 0.0 parts by weight of the amount of peroxide.
Compositions containing 5-5 times more of at least one cross-linking agent selected from the group consisting of 1,2-polybutadiene, triallyl cyanurate, triallyl isocyanurate are described. The preferred cross-linking agent for this cross-linking action is bis-(t-alkylperoxy or bis(t-alkylperoxyalkylbenzene)).
bis(t-butylperoxy)-2.5, dimethyl-hexane, and α. αbis(t-butylperoxyisopropyl)benzene.

According to the present invention, cross-linking agents, co-curing agents (co-curing agents)
A cross-linkable polyethylene composition has been discovered that consists of a sterically hindered phenolic antioxidant 1F agent and a second antioxidant.

According to the invention, therefore, polyethylene with a density of 0.920-0.970 g/cm3 and a melting coefficient in the range of to-35 dg/min, 0.3-1.3% by weight of polyethylene, is used.
bis(t-alkylbaroxyalkyl)benzene,
0 of polyethylene.

2-1.5% by weight of triallyl cyanurate, triallyl isocyanurate, and l.

a co-curing agent selected from the group consisting of 2-polybutadiene;
0.01-0.05% by weight of polyethylene-hindered phenolic antioxidant, 0.01% of polyethylene
-0.2 % double edges of di(stearyl)-pentaerythritol diphosphite, tris-di(t-butylphenyl) phosphite, dilaurylthiodipropionate, and bis(2,4-di-butylphenyl) A composition is provided comprising a second antioxidant selected from the group consisting of pentaerythritol diphosphite.

In a preferred embodiment of the invention, the peroxide is bis(
t-butylperoxyisopropyl)benzene.

According to the invention, a melting coefficient of 1010
Density 0.920-0.970g in the range of -35d minutes
/cma of polyethylene, 0.3-1.
311% by weight of bis(1-alkylperoxyalkyl)
benzene, 0.2-1.51 i% of polyethylene, a co-curing agent selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, and 1,2-polybutadiene, 0.01-0 of polyethylene゜05il
% of sterically hindered phenolic antioxidant fF agent, 0.01-0.2% of polyethylene, di(stearyl)-pentaerythritol diphosphite, tris-di(
a second antioxidant selected from the group consisting of t-butylphenyl) phosphite, dilauryl thiodipropionate, and bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite; An improved method is provided.

The polyethylene used in the composition of the present invention has a density of 0.
920-0.970g/cm, especially 0°950-0.9
70g/cm polyethylene. The density of polyethylene will depend, among other things, on the intended end use of the composition; whether polyethylene is a homogeneous polymer of ethylene;
Or ethylene and a small amount of C, -C,. α-olefin,
For example, it can be a copolymer of ethylene and small amounts of butene-12hexene-1 or octene-1. Methods for making such polymers are known in the art.

Polyethylene has a melting coefficient of 110-35 d/min, especially 1
It is in the range of 16-26 d/min. Melting coefficient is ASTM
Measured according to D-1238 (condition E).

The composition of the present invention contains 0.3-1°3% by weight of polyethylene.
bis(t-alkylperoxyalkyl)benzene,
Contains 0.4-0.9i% peroxy compounds of polyethylene. A preferred peroxide is bis(t-butylperoxyisopropyl)benzene. Such peroxides are commercially available from Herculus under the trade name Vulcup.

Peroxides can be used in various forms, for example in pure form or supported on an inert carrier such as clay. Both forms of peroxide are commercially available.

In addition to peroxides, the compositions of the present invention also contain co-curing agents selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, and 1,2-polybutadiene. 1.5! Contains the amount%. In a preferred embodiment, polyethylene 0,4
-0, heptad% triallyl cyanurate or triallyl isocyanurate as a co-curing agent.

The composition of the present invention contains two antioxidants. 1st
These are sterically hindered phenolic antioxidants, such as those used commercially to stabilize polyethylene. Sterically hindered phenolic antioxidants are 0.01-0.05, especially 0.01-
It can be used in an amount of 0.03% by weight. Examples of suitable sterically hindered phenolic antioxidants include ophtadecyl-3,5-di-t-butyl-4-hydroxycinnamate and tetrakis-methylene-3-(3',
5°-di-t-butyl-4-hydroxyphenyl)propionate methane.

The antioxidants in gA2 are di(stearyl)-pentaerythritol diphosphate, tris(di-t-butylphenyl) phosphite, dilaurylthiodipropionate and bis(2,4-di-t-butylphenyl)pentaeryth It is a little diphosphite. The second antioxidant is 0.01-0.2, especially 0.06-0 of polyethylene.
．． It can be used at 1% by weight.

As will be shown below, each component of the present invention is essential to producing rotomolded products with acceptable end uses. However, when polyethylene is cross-linked using the peroxides of the compositions of the present invention but in the absence of other specified components, the resulting rotomolded articles tend to have unacceptable properties. . In particular, the resulting product is prone to bubble formation in containers made from it, and leaks to the extent that they are unable to hold liquid. ) The peroxides chosen in the K invention are acceptable peroxides that do not pose potential health risks when used in the cross-linking of polyethylene, especially with regard to skin and eye irritation issues.

Co-curing agents are used in the compositions of the present invention to suppress the formation of bubbles. Examples of the use of various co-curing agents for cross-linking polyethylene in rotomolding processes are shown in the Examples below. The two co-curing agents most effective at inhibiting bubble formation are trialkyl cyanurates and trialkyl isocyanurates.

Geologically impaired phenolic antioxidants are used for the same reasons that antioxidants are used in typical end uses of polyethylene. Such antioxidant 2F agents reduce oxidation of polyethylene when exposed to environmental conditions during processing, such as during rotational molding, or in subsequent end use.

The second antioxidant 1F agent is used to impart improved end-use properties, particularly to improve low temperature impact properties. Four secondary antioxidants, namely di(stearyl)-pentaerythritol diphosphite, tris-di(t-butylphenyl)phosphite, dilaurylthiodipropionate, and bis(2,4-di-t -butylphenyl) pentaerythritol diphosphite can be used. A preferred second antioxidant is trisdi (t
-butylphenyl) phosphite. because,
This is because the use of this second antioxidant tends to produce rotomolded articles with improved color. This antioxidant is manufactured by Ciba-Geig Canada (Ciba-Geig Canada).
y Cana da) N L to Arga 7 #s (I
It is commercially available under the trade name RGAFOS) 168. Such compositions are available as powders rather than pellets.
Especially N.

It is preferably used in the form of a powder that passes through a 32 mm Tyler mesh sieve.

The composition can be made by feeding polyethylene in the form of pellets into an extruder, in particular an extruder fitted with a suitable mixing screw. Handicapped phenolic antioxidants are usually incorporated into the polyethylene before it is fed to the extruder, especially during polyethylene production. The remaining additives can be compounded with the polyethylene using concentrates and/or by metering the additives into the extruder, eg, through the barrel of the extruder. In particular, additives use carriers.

In particular, the composition of the present invention can be metered into an extruder using paraffin oil as described in Canadian Patent No. 957,473 of H.J. Cook dated November 12, 1974. The material can be converted into a form suitable for rotational molding by methods known in the art, such as by milling the pelletized composition of the invention.

Molded articles can be made from the compositions of the invention by rotomolding. In rotational molding, a polymer, usually in powder form, is fed into a mold which is then rotated. The composition is heated to a temperature such that it forms a substantially uniform layer of molten polymer in the mold. If the temperature is increased further, the polymer of the composition of the present invention will undergo cross-linking. When rotomolding the composition of the present invention, the temperature of the rotomolding furnace is approximately 260-350°C.
must be within the range of

Higher temperatures and/or heating at higher temperatures for longer periods of time will result in unacceptable, eg, browned products, as known in the art.

In a preferred embodiment, the rotomolding process is performed such that the gel content of the polymer of the molded article is at least 75%, in particular 80-90%.
In this specification, the gel is operated so that xylene is used as the solvent and the extraction apparatus is
refers to the material that remains after Soxhlet extraction of polyethylene using a Tyler Metsch sieve.

Molded articles made from the composition of the present invention by rotational molding can be used for various applications, such as gasoline tanks, barrels, containers, storage tanks, etc. The composition of the present invention can also be used for Used as drum liners or in the pipe and wire coating industry.

The following examples illustrate the invention.

Example 1 A number of inventive and control crosslinkable compositions were prepared. Powdered polyethylene containing a sterically hindered phenolic antioxidant was mixed in a high speed laboratory mixer. The resulting mixing portion was melt-blended using a single screw extruder at a melting temperature of 140°C. The extrudate from the extruder was pelletized and then ground into a fine powder commonly used in rotomolding.

A powder of an acid is placed in a stationary mold whose L part is open to air and heated from the bottom. The temperature of the mold was increased from ambient temperature to approximately 20°C for approximately 20 minutes.
The molded product is then cooled to a thickness of 511I.
11, a disk with a diameter of 50 mm was poked.

The details of the experiment and the results obtained are summarized in Table 1.

Example 2 Four crosslinkable polyethylene compositions of the present invention were
The components of the composition were melt compounded using a 60 III 11 single screw extruder. The polyethylene is fed in the form of petlets into the hopper of the extruder, while the remaining ingredients are injected in liquid form through a boat on the side of the extruder. The extrudate obtained from the extruder is cut into pellets and then ground into N005 Tyler (T
yler) Grind into a powder that passes through a mesh sieve.

This powder was rotomolded in an oven maintained at a temperature of 288°C to form 14.2-pack boxes with 0.33 cm wall thickness and 5 gallon sherry with 0.44 cm wall thickness. I made it.

Fill 12 cans with ethylene glycol to make rice sherry.
After cooling to 5° C., the cans were tested by dropping them from a height of 6.1 m.

The details of the experiment and the results obtained are summarized in Tables 2 and 3.

Example 3 Two crosslinkable polyethylene compositions were made by the method of Example 2. In one composition the polyethylene was Sclair 2910 polyethylene and in the other it was Sclair 2911 polyethylene. The details will be described later. Both polyethylenes contain phenolic antioxidants that are stereotoxic. The additives used in these compositions were as follows (all proportions are by weight):

Vulcup RO, 5% peroxide triallyl cyanurate 0.5% mineral oil
0.5% ar is 7 male (I rg
af o s) 0.075% 168 -oxide Drums with a volume of 33 gallons were made from each composition using industrial rotomolding equipment with an oven temperature of 268-288°C. The gel content of the drum thus obtained is 80-9, depending on the cycle time of the rotomolding process.
It was 0%. The drum contained no holes or air bubbles.

This drum was filled with a glycol solution at a temperature of -21°C and dropped from a height of 4 m. There was no damage to the drum due to the impact.

Example 4 A crosslinkable polyethylene composition was made according to the method of Example 2. This polyethylene is Sflare (Sc
lair) 2910 polyethylene, and the additives used in this composition are as follows (all percentages are according to Seiso).

Vulcup RO, 4% peroxide triallyl isocyanurate 0.4% mineral oil
0.5% Argaphos (Irga
fos) 0.07% 168 peroxide A storage tank with a wall thickness of 7.5 mm and a capacity of $14,100 was rotationally molded from this composition at an oven temperature of 315° C. and a curing time of 24 minutes. The walls of the resulting tank were free of air bubbles and the gel content of the polymer was 84%.

A 10cm x locm board from the tank wall! ,
I) It was sampled, cooled to -40'C, and subjected to an impact test using a dart with a diameter of 2.5 cm and a weight of 6 kg.

When a dart was dropped from a height of 3 m onto the L of the board, the board did not break at all.

Example 5 A crosslinkable polyethylene composition was made by the method of Example 2. This polyethylene is Sflare (Sc
lair) 2910 polyethylene, and the additives used in this composition are as follows (all percentages are according to Juken).

7) L! Vulcup RO, 55% Peroxide Triallyl Isocyanurate 0.55% Mineral Oil
Borg 0.07% Warner (Borg-
A cross-linkable resin of bis-(2,4-di-t-butylphenyl)pentaerythritone rephosphate powder commercially available from Warner, Inc. was rotomolded to a wall thickness of 0.6.
I made a box of 3 cm and 14.2 sentences. 1 diameter from the wall of the box
Cut out a 0cm plate, cool it to -40℃, and cut it to a diameter of 2.5cm.
An impact test was conducted using a dart weighing 6.5 kg and weighing 6.5 kg. Even when a dart was dropped onto the board from a height of 3 meters, the board did not sustain any damage.

Table 1 Notes This experiment 1 and 2 are control examples.

Zero* Here, a hole refers to a hole that partially passes through the disk and /nu completely passes through the disk.

IJ, Pasol (LUPER3OL) 130:2.5
-dimethyl-2,5-di(t-butylperoxy)hexyne-3, Klass and Tianayne (Wal 1
Ace and Tiernan) product name.

Guicup (DI CUP) R: dicumyl peroxide,
A product name of the Hercules company.

DIAK-7: ) Reallyl isocyanurate, E.I. du Bon de Nemoise (
E.1. du Font de Nemours
) company's product name.

DLTDP: Diallylthiobrobionate.

HVA 2: N, N'-m-7x nylene diamine, E.
Product name of Font de NemourS).

Arca'7ts (IRGAFO5) 168: To! J
Di(t-butylphenyl) phosphate, trade name of CI ha-Geigy.

RICON 150: l, 2-polybutadiene (molecule #2000), Colorado Chemical Specialty 4
5speciality) product name.

RICON 154: Polybutadiene (min. 71
+l:3000), Colorado Chemical Φ Specialty (Colorado Chemical 5p
Product name of company (eciality).

CHEMLINK 30: ) Limethylol propane/trimethyl acrylate, trade name of Ware Chemical Company.

Table 2 Box molding self-momme game Notes for Table 2 A = Nuclea 2910 polyethylene, Density 1N0
, 960 d g/cm3. Melting coefficient 18dg/min 9w
Contains 0.025% of harmful phenolic antioxidants, manufactured by Du Bont Canada.

Zero B = Nisflare 2911 polyethylene, same as A,
However, the melting coefficient is 25 d g 1 minute.

At the end of the book, the intensity coefficient is Hunter ■D-2
It was measured using a type 5 optical sensor W, type L/a/b color/color difference spectrometer.

Table 3 (Sherry can molding)

Claims (1)

[Claims] 1. Density 0 with a melting coefficient in the range of 110-35 d/min.
．． 920-0.970 g/cm" of polyethylene, 0.3-1.3% by weight of polyethylene bis(t-alkylperoxyalkyl)benzene, 0.2% of polyethylene
- 1.5% by weight of a co-curing agent selected from the group consisting of triallyl cyanurate, triallyl isocyanurate, and 1.2~polybutadiene;
．． 01-0.05. % sterically hindered phenolic antioxidants, 0.01-0.2% by weight of polyethylene, di(stearyl)-pentaerythritol diphosphite, tris-di(t-butylphenyl)phosphite, dilauryl thiodipropionate, and bis(
A composition comprising a second antioxidant W agent selected from the group consisting of 2,4-';-t-butylphenyl)pentaerythritol diphosphite. 2. The composition according to claim 1, wherein the co-curing agent is 1,2-polybutadiene. 3. The composition according to claim 1, wherein the co-curing agent is triallylcyanurate or triallylcyisoanurate. 4. The composition according to claims 1 to 3, wherein the co-curing agent accounts for 0.4 to 0.7% of the polyethylene. 5. The composition according to claims 1-4, wherein the polyethylene is a homogeneous polymer of ethylene. 6. The composition according to claims 1-4, wherein the polyethylene is a copolymer of ethylene and an α-olefin of ca-Cto. 7. Density of polyethylene is 0, 950-0, 970
g/crn'. 8. The composition according to claims 1 to 7, wherein the peroxide is bis(t-butylperoxyisopropyl)benzene. 9. Claim 1- where the antioxidant in @2 is di(stearyl)-pentaerythritol diphosphite.
Composition according to item 8. 10. The composition according to claims 1-8, wherein the second antioxidant is tris-di(t-butylphenyl)phosphite. 11. The composition according to claims 1-8, wherein the second antioxidant is dilaurylthiodipropionate. 12. The composition according to claims 1-8, wherein the second antioxidant is bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite. 13. The composition according to claims 1-12, wherein the peroxide bar is 0.4-0.9% by weight of polyethylene. 14. Bol Jx tyrene density is 0.950-0°970
g/cm3. Peroxide is 0.4-0.9 of polyethylene
The above percentage of bis(t-butylperoxyisopropyl)benzene, co-curing agent acid is 0.4-0.7 of polyethylene.
% by weight, and the second antioxidant is tris-di(t-butylphenyl) phosphite. 15. In the rotational molding process for manufacturing products of polyethylene compositions, polyethylene with a melting coefficient in the range of 110-35 d/min and a density of 0.920-0°970 g/Cm3, 0.3-0.3- of polyethylene 1.3% by weight of bis(t-alkylperoxyalkyl)benzene, 0.2-1.5% by weight of polyethylene, triallyl cyanurate, triallyl isocyanurate, and 1.
a co-curing agent selected from the group consisting of 2-polybutadiene;
0.01-0.05i% of polyethylene sterically hindered phenolic antioxidant, agent, 0.0% of polyethylene
1-0.2ii% of di(stearyl)-pentaerythritol diphosphite, trisdi(t-butylphenyl)phosphite, dilaurylthiodipropionate,
and a second antioxidant selected from the group consisting of bis(2,4-di-t-butylphenyl)pentaerythritol diphosphite. 16, Po') X-chi L/7 (7) Density is 0.95
Claim 15 which is 0-0°970g/cm3
The method described in section. 17. The method according to claim 16, wherein the co-curing agent is 1,2-polybutadiene. 18. The method according to claim 15 or 16, wherein the co-curing agent is triallyl cyanurate or triallyl cyanurate. 19. The method according to claims 15-18, wherein the peroxide is bis(t-butylperoxyisopropyl)benzene. 20. The density of polyethylene is 0.950-0°970g
/cm3. The amount of peroxide is bis(t-butylperoxyisopropyl)benzene of 0.4-0.9 weight percent of polyethylene, the amount of co-curing agent is 0.4-0.7 weight percent of polyethylene, and 19. The method according to claim 15 or 18, wherein the second antioxidant is tris-di(t-butylphenyl) phosphite. 21. A method according to claims 15-20, wherein the gel content of the product obtained is at least 75% by weight.